1. Field of the Invention
The present invention relates to a gas turbine intake air filter unit, more specifically to improving technique of a filter unit for efficiently collecting dust contained in outside air aspirated into a gas turbine.
2. Description of the Related Art
As is popular in the industry, a gas turbine is provided with an intake air filter unit at an upstream side end portion of an intake duct communicating with an internal area of the gas turbine, for collecting fine dust contained in outside air aspirated by an air compressor. Since it has been a conventional understanding that operation of the air compressor would not be seriously disturbed provided that the intake air filter unit is capable of collecting dust of a particle diameter of approx. 5 xcexcm or larger, a two-stage intake air filter unit having two filter layers has conventionally been employed.
However, in such two-stage intake air filter unit, minute dust of a particle diameter of for instance less than 1 xcexcm that can pass through the filter layers adheres to a vane of the air compressor, leading to lower performance of the air compressor and further to a substantial output loss of the gas turbine, and resultantly the gas turbine cannot satisfy current demand for a high output. Employing filter layers having a higher collecting efficiency in the two-stage intake air filter unit could be a solution of the problem, however such a simple measure only causes disadvantages such as a shorter life span of the filter layers and need for frequently replacing the filter layers in short intervals. Besides, when replacing the filter layers operation of the gas turbine must be suspended in order to prevent intrusion of dust into inside the gas turbine, therefore availability factor of the gas turbine inevitably becomes lower.
Accordingly, as disclosed in JP-A No.7-253028, recently a three-stage intake air filter unit having three filter layers has been proposed, and has come to be put to trial. The filter unit disclosed in this Publication comprises a primary filter layer constituted of a panel type demister and a rolled strap type or streamer type prefilter, a secondary filter layer constituted of medium performance filters and a tertiary filter layer constituted of high performance filters, sequentially aligned from an upstream side in a direction of intake air flow.
In this case the panel type demister comprises unitary demisters formed into a plate shape by coating and bonding with a binder a multitude of small elastic bodies made of animal and vegetable fibers curled into a spring shape, and four rows of four pieces each, totally 16 pieces of such unitary demisters are disposed inside a casing located at an upstream side end portion of the intake duct.
Also, the rolled strap type and the streamer type prefilter are unitary filters made of a glass fiber or organic fibers such as acrylic fiber etc. The rolled strap type prefilter comprises a strap-shaped fiber filter medium spanned between a pair of rolls on which the fiber filter medium can be rolled, while the streamer type prefilter comprises a multitude of bags disposed in parallel close to one another with the respective openings fixed to a frame, and four rows of four pieces each, totally 16 pieces of either of such prefilters disposed inside the casing constitute the primary filter layer.
Further, the medium performance filter and the high performance filter are unitary filters comprising a high efficiency filter medium and a low efficiency filter medium closely layered, bent in zigzags with the projections and recesses thereof aligned with a direction of intake air flow and then set in a box, and four rows of four pieces each, totally 16 pieces of such unitary filters disposed at two positions inside the casing respectively constitute the secondary filter layer and the tertiary filter layer.
With respect to the foregoing three-stage intake air filter unit, in all of the primary filter layer, secondary filter layer and tertiary filter layer, the prefilters, medium performance filters and high performance filters that are the unitary filters of the respective filter layers are disposed on a plane that is orthogonal to a direction of intake air flow inside the intake duct, as shown in FIG. 1 of the aforementioned Publication.
More specifically, in the primary filter layer totally 16 pieces of the rolled strap type or streamer type prefilters are disposed on an identical plane, in the secondary filter layer totally 16 pieces of the medium performance filters are disposed on an identical plane, and in the tertiary filter layer totally 16 pieces of the high performance filters are disposed on an identical plane.
Under such configuration wherein the unitary filters are disposed on a plane in all of the filter layers, however, when the filter layers are increased from two stages to three stages, flow resistance hence pressure loss of the intake air passing through the tertiary filter layer may become unreasonably great because of insufficient intake air passing area of the tertiary filter layer, thereby disturbing smooth flow of the intake air and resultantly causing driving loss of an air compressor.
Accordingly a balance of collecting efficiency of the tertiary filter layer and intake air flow resistance becomes a critical issue to be explored, however at present development of an intake air filter unit focused on optimization of such balance has not yet been achieved, because of which such problems as adherence of minute dust to an air compressor and reduction of life span of filters and so forth have not been effectively solved.
In view of the foregoing problems, it is a technical object of the present invention to provide a gas turbine intake air filter unit, wherein flow resistance of intake air passing through a tertiary filter layer does not become unreasonably great despite the filter layers are increased from two stages to three stages, and a balance of collecting efficiency of the filter layers and the intake air flow resistance is optimized.
In order to solve the foregoing technical problem, the invention provides a gas turbine intake air filter unit, comprising a primary filter layer, a secondary filter layer, and a tertiary filter layer placed at an upstream side end portion of an intake duct that leads intake air into an internal area of a gas turbine and sequentially aligned from an upstream side; wherein the primary, secondary and tertiary filter layers respectively include a plurality of unitary filters; and the plurality of unitary filters of the tertiary filter layer are aligned in such a manner that at least a recess is formed toward a downstream side of the intake air flow.
Under such constitution, since the plurality of unitary filters in the tertiary filter layer are disposed so as to include at least a recess toward a downstream side of the intake air flow, intake air passing area is increased in proportion to the area of the recessed portion. Accordingly, increase of flow resistance, hence pressure loss of the intake air through the tertiary filter layer is properly restrained, therefore smooth flow of the intake air is secured and driving loss of the air compressor is prevented. Moreover, a balance of collecting efficiency of the three filter layers and the intake air flow resistance becomes extremely favorable, therefore adherence of minute dust to the air compressor and reduction of life span of filter layer can be effectively avoided. In addition, since the recess is formed in a direction of downstream side of the intake air flow, there is no likelihood of interference with the secondary filter layers located at an upstream side of the tertiary filter layer, and an optimum layout of the three filter layers can be maintained.
In this case, it is preferable that a downstream side end portion of the recess is located at an upstream side of a wind velocity reference line serving as an index of whether or not a turbulent flow of intake air causes noise and/or vibration. Here, the wind velocity reference line stands for a reference line by which to distinguish whether or not noise and/or vibration is generated in the tertiary filter layer by a turbulent flow of the intake air when the intake air flows into the intake duct from the filter unit, and specifically the reference line is an index showing whether or not flow velocity of the intake air inside the filter unit exceeds 5.7 m/sec. And since the intake air flow velocity is relatively slow in an upstream side area of the wind velocity reference line, such area is naturally an area where the noise or vibration is not generated. Consequently, such constitution effectively prevents generation of noise or vibration in the tertiary filter layer due to a turbulent flow of the intake air, while effectively maintaining the above described various advantages of forming a recess toward a downstream side in the tertiary filter layer.
Also, it is preferable that the recess is disposed so as to confront an upstream side end opening of the intake duct. By such configuration the recess of the tertiary filter layer falls on a path that a main stream of the intake air flowing toward the intake duct is passing through, i.e. a path where the intake air flow amount is the largest, therefore the intake air passing area is increased at an area where clogging by dust is most likely to take place. As a result, clogging by dust and increase thereby of flow resistance in the tertiary filter layer can be efficiently avoided.
In all the foregoing constitutions, it is preferable that the primary, secondary and tertiary filter layers are formed so as to cover the upstream end opening of the intake duct in a bag shape. Under such configuration, when the intake air flows into the intake duct through the primary, secondary and tertiary filter layers one after another, the intake air is introduced from various directions including a lateral portion of the intake air filter unit, in addition to an upstream side end portion of the intake air filter unit along the intake air flow direction inside the intake duct. Therefore, the intake air passing area of the three filter layers is substantially increased, and as a result untimely increase of the intake air flow resistance due to clogging by dust etc. can be restrained, and sufficient intake air passing area can still be secured by making the intake air filter unit more compact in dimensions. Also, in case where the primary, secondary and tertiary filter layers are formed in a bag shape, though a room for the tertiary filter layer inevitably becomes smaller compared with the primary and secondary filter layers, since a recess is formed in the tertiary filter layer as already described which is making the intake air passing area larger, unreasonable increase of the intake air flow resistance by having to pass through the tertiary filter layer can be effectively restrained.
Also, in the foregoing constitutions, it is preferable that each of the unitary filters of the primary filter layer and of the secondary filter layer is insert-fitted to a first fixing frame, and that each of the unitary filters of the tertiary filter layer is insert-fitted to a second fixing frame. In case where a recess is formed in the tertiary filter layer as above, the second fixing frame is formed in a bent shape according to a shape of the recess, while when the respective filter layers are formed in a bag shape the first fixing frame and the second fixing frame are respectively formed in a bent shape according to respective shapes of the filter layers. Consequently, providing only two fixing frames despite there are three filter layers contributes to reduction of number of parts, simplification of assembly and cost-saving.
Further, in the foregoing constitutions, it is preferable that a weather louver for integrating and refracting intake air flow is located at an upstream side of the primary filter layer. Under such arrangement, even when outside air contains rain water or mist the weather louver prevents such liquid from penetrating into the filter unit, therefore especially the primary filter layer can be kept from adherence of liquid, which results in a longer life span of the filter layer and prevention of corrosion inside the gas turbine.
In this case, it is preferable that the weather louver is formed so as to cover the upstream end opening of the intake duct in a bag shape. As a result of such arrangement, since the weather louver covers the entire area of the respective filter layers in case where the filter layers are formed in a bag shape as described above, the weather louver properly follows up a shape of the filter layers so as to securely restrain penetration of rain water etc.